Produce two different metal salts (NaHSO4 and Na2SO4) through an application of specific stoichiometric ratios in a reaction of diprotic sulfuric acid (H2SO4) with sodium hydroxide (NaOH).

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Introduction

IB Chemistry - Practical Report Name: Chris Bolton Partner: Jamie Gearing Date(s) Conducted: 20/08/04 Topic: Acids and Bases Experiment: Neutralisation of Polyprotic Acids Aim: To produce two different metal salts (NaHSO4 and Na2SO4) through an application of specific stoichiometric ratios in a reaction of diprotic sulfuric acid (H2SO4) with sodium hydroxide (NaOH). Apparatus: Refer to attached worksheet for given apparatus and materials Method: Refer to attached worksheet for given method AMMENDMENTS/ADDITIONS/SAFETY PRECAUTIONS: * Avoid adding excess solution to evaporating basins whilst hot, as this may cause damage to the basins * Evaporate only a small volume of the evolved acids to reduce time required to produce the stock solution * Note: as acids evaporate small quantities of the salt may splatter - ensure that safety glasses are on securely * Do not add distilled water (for the stock solution) directly to the basins, rather wait momentarily for some cooling to occur * Agitate evolved solutions prior to evaporation to ensure homogeneity * To test the ?pH of NaHCO3, add a [small] sample to a [small] volume of distilled water and test the resulting solution with litmus Preliminary Calculations: Prior to commencement of the experiment, several preliminary calculations were necessary (stipulated by steps 2 and 3 in method). First it is necessary to find the number of moles in each 20.00 cm3 aliquot of sodium hydroxide using the known concentration. Given concentration is obviously necessary; [NaOH] = 1.0010 mol.dm-3 (accuracy must be assumed) ...read more.

Middle

Data Processing and Presentation: Responding to Processing Questions A. Defining mono/di/polyprotic acids: a) monoprotic; An acid capable of donating only one proton (H+ ion) during a reaction. Examples of monoprotic acids include: * hydrochloric acid (HCl); * nitric acid (HNO3); * ethanoic acid (CH3COOH) These acids only react in one stage in donating their proton - for example: HCl(aq) + H2O(l) ? H3O+(aq) + Cl-(aq) A B A B In this example the acid (HCl) donates a single proton to the water molecule, forming hydronium and anionic chlorine. b) diprotic; An acid capable of donating two protons (H+ ions) during a reaction. Examples of diprotic acids include: * sulfuric acid (H2SO4); * carbonic acid (H2CO3); * sulfurous acid (H2SO3) These acids can react in two stages, donating both their protons - for example: H2SO4(aq) + H2O(l) ? HSO4-(aq) + H3O+(aq) A B B A HSO4-(aq) + H2O(l) ? SO42-(aq) + H3O+(aq) A B B A In this example the acid (H2SO4) donates two protons to the water molecules, forming hydronium and anionic sulfate. c) polyprotic; this is a general term for an acid capable of donating two or more protons (H+ ions) during a reaction. Examples of polyprotic acids range in protenicity: * diprotic - sulfuric acid (H2SO4); * triprotic - tri hydrogen phosphoric acid (H3PO4); Polyprotic acids can react in quite a number of stages, donating however many feasible protons they have - for example: H3PO4(aq) + H2O(l) ...read more.

Conclusion

0.01 cm3 error with the pipette. These uncertainties have been included in calculations above without working. *NOTE: Since relatively small masses are involved, even a minute error of ? 0.01 cm3 becomes significant It is likely that a culmination of these errors - with an emphasis on the possibility of gross error in a miscalculation/measurement - could cause a variation to these results. Regardless, the results confirmed theoretical predictions quite confidently; the ratio's determined and measured yielded theoretically predictable products. Improvements: Several aspects of this experiment could be developed to yield more definitive results. The influences of random and systematic errors in this experiment were essentially insignificant. Key improvements to this experiment would, however, include: a) Use equipment consistently calibrated for a specific temperature and pressure (i.e. SLC) and maintain conditions at their calibration specifications b) Agitating solutions directly prior to evaporation and preparation of stock solutions c) Taking greater care to maintain burette vertically d) Ensure that all apparatus is rinsed with distilled water when appropriate to ensure that all the acid and base react e) Collation of multiple results, or repetition of experiment to ensure a more accurate average volume for each titre f) Pooling and compiling results to achieve a more precise average g) Allow more time for evaporation and use a larger quantity the acids to produce a more concentrated stock solution for testing h) Test gas evolved in reaction between NaHSO4 and Na2CO3, ensuring that it is CO2 to experimentally confirm theoretical reaction. If these improvements were implemented, the results would prove more definitive - there would be further proof of the theoretical expectations. Chris Bolton ...read more.

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